Let’s look at what goes on in the brain during sex and orgasm. Although you may think everything happens between your legs, the experience of orgasm actually occurs between your ears. All thoughts, feelings, and bodily sensations you have correlate with specific nerve cells being activated. Orgasm, like all experiences, is brought about by electric impulses flowing along paths of connected nerve cells. Orgasm happens when specific pleasure pathways are turned on, while your defense pathways are turned off.

All this happens by means of chemical messengers and the nerve cell receptors they bind to. These neurochemical changes take place primarily in the limbic system, a very old part of the brain with circuitry that is common to all mammals. These ancient limbic circuits control almost all bodily functions.

The limbic system's job is to keep you alive and reproducing. It does this by avoiding pain and repeating what is pleasurable. The limbic system is the seat of emotions, drives, impulses and desires—including sexual ones. It’s where you fall in and out of love…or lust. Due to the nature of the limbic system, you cannot will your feelings, emotions, falling in love, or staying in love, anymore than you can will your heart to beat, or yourself to digest a meal or sleep. The limbic system has been around for well over 100,000,000 years, lurking right beneath your large, rational neo-cortex.

Rats, apes and humans use the same neurochemicals to operate the same functions in this part of the brain. Keep in mind that scientists aren't studying rodent brains to help them with their addictions and erections! Studying animals and humans, scientists have begun to unravel the neurochemistry of lust, attachment and falling in love. Falling in love involves simultaneous activation and deactivation of discrete parts of the limbic system. For every biological event in your body, there is a biological cause. In this case, the cause is neurochemicals—and the pathways they turn on and off.

Neurochemical Commands: Your World Revolves Around Dopamine

The central neurochemical player behind falling in—and out—of love is dopamine. Dopamine is the principal neurochemical that activates your reward circuitry, the centerpiece of the limbic system. Your reward circuitry drives nearly all of your behaviors. In other words, most all roads lead to Rome, or to the reward circuitry, so you can assess things as "good, bad, or indifferent."

At its most basic, this circuit is activated when you engage in activities that further your survival, or the continuation of your genes. Whether it’s sex, eating, taking risks, achieving goals, or drinking water, all increase dopamine, and dopamine turns on your reward circuitry. You can think of dopamine as the "Gotta have it!" neurochemical, whatever "it" is. It’s the "craving" signal. The more dopamine you release and the more your reward circuit is activated, the more you want or crave something.

A good example is food. We get a much bigger blast of dopamine eating high-calorie foods than we do low-calorie foods. It’s why we choose chocolate cake over Brussels sprouts. Our reward circuit is programmed so that "calories equal survival." You’re not actually craving ice cream, or a winning lotto ticket, or even a romp in the sack. You’re craving the dopamine that is released with these activities. Dopamine is your major motivation, not the item or activity.

Dopamine is not the only neurochemical involved with reward, but it’s the one that motivates you to go after the reward. Dopamine governs the feelings of wanting, yet the experience of liking or enjoying something is probably due to opioids. Opioids are your brain's own morphine and endorphins. Dopamine drives us toward eating or orgasm, but the experience of the actual orgasm or eating chocolate arises from opioids goosing the reward circuit. In essence, dopamine is never satisfied.

Addiction mechanisms are extraordinarily complex, and not fully understood. Yet the one aspect they share is dopamine [7] dysregulation. All addictive substances and activities share one thing – the ability to strongly elevate dopamine levels. Watching porn, accumulating money, gaining power over others, gambling, compulsive shopping, video games…if something really boosts your dopamine, then it’s potentially addictive for you. Why did Martha Stewart risk everything for more money? She got a thrill from a stock market gamble. She didn’t need the money; she (thought she) needed the dopamine.

Addictive highs mimic the good feelings of the basic activities for which we're actually wired...by hijacking our reward circuitry. Only a few substances (alcohol, cocaine, etc.) have the ability jack up dopamine – that’s why they are addictive. We can also hijack it with extremely stimulating versions of natural behaviors: casinos with hot hostesses, novel porn at every click, tasty junk food filled with fat and sugar, and so forth. Dopamine especially responds to novelty and the unexpected, among natural stimuli.

Don't fall into labeling dopamine as bad. There's no such thing as a bad neurochemical or hormone, although either can become a problem when out of balance. Dopamine is absolutely necessary for your decision-making, happiness, and survival. Yet when it’s too low or too high (or when changes in its receptors alter your sensitivity), it can cause real problems. If you look at this chart you can see some behaviors and conditions associated with dopamine levels or with sensitivity to dopamine. Sensitivity equates with how many receptors a nerve cell has for dopamine.

It's true that some of the conditions listed are at extreme ends of the dopamine spectrum. Nonetheless, dopamine is involved with many aspects of mood, behavior, and perception. Even small shifts in dopamine sensitivity or levels can have profound effects on how you see the world, or your partner.

The key word on the list below is bonding. Bonding is more than a behavior. It is a mammalian program, the program that permits parenting and living in groups. When dopamine drops, you are likely to find your partner less rewarding—and your bond unravels.

Dopamine Levels (or altered sensitivity to dopamine)

Excess

Deficient

"Normal"

Addictions

Addictions

Healthy bonding

Compulsions

Depression

Feelings of well-being, satisfaction

Mania

Anhedonia—no pleasure, world looks colorless

Pleasure, reward in accomplishing tasks

Sexual fetishes

Lack of ambition and drive

Healthy libido

Sexual addiction

Inability to bond

Good feelings toward others

Unhealthy risk-taking

Low libido

Motivated

Aggression

Erectile dysfunction

Healthy risk taking

Psychosis

Social anxiety disorder

Sound choices

Schizophrenia

ADHD or ADD

Realistic expectations

Sleep disturbances, "restless legs"

Parent/child bonding

Contentment with "little" things

The power of dopamine and our reward circuitry are seen in classic experiments done on rats. Consider what happens when sadistic scientists put a starving rat on one side of a grid with electric current running through it and food on the other side. The rat will not cross the pain-producing grid. Yet put a rat with an electrode planted in her reward circuitry on one side of the grid and a lever she knows will stimulate her reward circuitry on the other, and she’ll dash across the grid to tap that lever nonstop. Stimulation of her reward circuitry becomes her top priority, because it’s telling her inner compass that a big reward is just around the corner. She will ignore food, even if starving, or abandon her unweaned pups just to tap that lever until she drops.

If the rat is male, he’ll ignore a receptive female to tap it until he drops. Humans implanted with similar electrodes (decades ago) experienced a constant urge to tap their levers, as well as intense sexual arousal—but not pleasure or orgasm itself. They also reported an undercurrent of anxiety.

Despite the obvious differences between rats and humans, rats have been called "guiding flashlights" for understanding the primitive mechanisms of our own brain.

Sexually-satiated male rats take up to fifteen days[8] to recover their full desire for sex (although they can get it up long before they are back to full steam). Meanwhile, even if they're feeling sexually sluggish, there is a reliable way to jump-start them, which we’ll get to in a moment. (Female rats also show evidence of a similar cycle[9] in the form of predictable surges of prolactin after vigorous copulation, whether or not they become pregnant. A shadow version of this prolactin cycle has now been detected in women[6], and may be connected with post-sex mood swings in some women.)

Research also shows that male rats experience a reduction in testosterone receptors[10] for up to a week within their reward circuitry. Hormones and neurochemicals dock with receptors on the nerve cells. In this case, fewer receptors mean less sensitivity to circulating testosterone. The result is that the reward circuitry pumps out less dopamine. It's like the reward circuitry's batteries are low. If this happens in females, it would also reduce their sexual desire.

Low testosterone (or decreased sensitivity to it) is associated with irritability and anger. Serotonin and endorphin levels also rise in the reward circuitry of sexually-satiated rats. Most of us have heard that these are "happy neurochemicals," but in this part of the limbic system both function to put on the brakes instead of just producing warm, fuzzy feelings. Keep in mind that sexual dysfunction is a major side effect of taking either antidepressants that raise serotonin or narcotics that mimic endorphins. When neurochemicals dampen your reward circuitry for a time, your relationship can suffer. See The Passion Cycle[11] for an overview of this neurochemical cycle, and for more recent research see Men: Does Frequent Ejaculation Cause A Hangover?[12] and Women: Does Orgasm Give You a Hangover?[6]

UPDATE (2014): Researchers have shown that ejaculation, even twice a week, shrinks the dopamine-producing neurons[13] in the VTA, which reduces a male's response to the pleasure of morphine. This also happens with repeated heroin use in both rats and humans. Scientists have also learned that amphetamine activates the exact same nerve cells[14] as orgasm, urging the brain to "remember and repeat." In other words, drugs of abuse "work" because they're hijacking the mechanisms[15] that evolved to make us want sex...and yet experience aftereffects from too frequent sex.

Dopamine and the Coolidge Effect

Humans, like virtually all mammals, are not naturally monogamous (as in sexually exclusive), although many individuals are. This may not sound very romantic, but no mammals are sexually exclusive. (A few, such as humans, are "socially monogamous." That is, they typically raise their offspring together.) It is therefore likely that our mating neurochemistry is set up to accomplish two goals. It encourages bonding so we co-parent.

Yet there is also a conflicting program to push us out of those bonds—at least far enough to add a novel mate. From chimps to rats, the same neurochemical events drive mammalian behaviors, and they are driving them to be promiscuous. Is it likely that Mr. and Mrs. Rodent are growing apart in their relationship? Could the excitement be gone from their marriage? Perhaps Mrs. Chimp spends too much money, or nags too much. Maybe Mr. Chimp watches too much football or doesn’t help much with housework. Not likely. Just like us, they have a subconscious program, triggered by mating, found in their limbic systems, which biology uses to urge them tire of their mates and move on to new mates.

During the week or two that the hangover from orgasm lingers, our large, rational brain proposes logical reasons to explain our relationship disharmony. Orgasm is natural…absolutely. But it may also be natural for both men and women to sour on a mate, to suddenly find a spouse unattractive, irritating, and wholly unreasonable. It may even be natural to become wholly unreasonable, and thus hasten the departure of a mate.

Now, we know that all of you are wondering about that sure-fire way to jump-start male rats' flagging libido. Perhaps you can already guess. All you have to do is introduce a new, receptive female. That may not be the answer you were hoping for…or perhaps it was!

Have you ever heard of the "Coolidge Effect?" Because that’s what we're addressing. Scientists have discovered that—after a frenzy of copulation—a male rat will lose interest in a female. BUT should a new female show up, he’ll perk up long enough to service her.1

This process of presenting novel mates to males can be continued until they practically die of exhaustion—once again proving that biology doesn’t give a rat’s…hindquarters about anything but propelling genes into the future.

The Coolidge Effect[16] has been observed in every species tested, and not just in males. Lady rodents prefer to seduce new guys, too. The Coolidge Effect just might play a role in human affairs as well. Marnia once talked with a man who had stopped counting at 350 lovers. He said, "I really don’t understand it. I lost interest in all of them sexually so quickly—and some of those women are really beautiful, too."

The Coolidge Effect is linked to your post-orgasm hangover. The reason the rat loses interest is that he’s getting a weaker and weaker dopamine surge from Partner No. 1. No dopamine surge, no interest. She is not perceived as "rewarding." The same thing happens to humans. The thrill is gone, and Partner No. 1 looks like Brussels sprouts. Now you’re primed for anything that will jack up your dopamine again. Partner No. 2 appears, and your dopamine soars. As if by magic, your blues are gone, and you have that heady feeling of anticipation, that sense of uninhibited aliveness. In short, No. 2 looks like chocolate cake. (This also has implications for understanding today's binging on Internet porn[17].)

Assuming we don't learn how to steer for lasting bonds[18] by taming our limbic system, our reward circuitry will push us to do just what it evolved to do (once our temporary honeymoon neurochemistry wears off). We'll get less and less dopamine "reward" during sex with our current mate. Notice that this is similar to what occurs when people use drugs, play intense video games, binge on Internet porn, or gamble. They seek more and more stimulation to get the same high. In short, feelings of sexual satiety do not promote romance—which calls into question a lot of today's relationship advice about producing bigger, better and more frequent orgasms.

The truth has been recognized for thousands of years. Here's a poem from the ancient Greek Anthology.

Once plighted, no men would go whoring.

They'd stay with the one they adore,

If women were half as alluring

After the act as before.

Back to our tale. What if No. 2 doesn’t show up for your tryst, and you’re left in the doldrums? Unlike rats, you have many dopamine-raising possibilities—from Internet porn, gambling and alcohol, to the dopamine agonists drug companies are producing to light a fire under slumbering libidos (not recommended, due to risky side effects). These "fixes" make you feel better briefly, but as far as your well-being goes, they are like eating junk food—a net loss. As biologist Robert Sapolsky observed, there is a price for blasting our reward circuitry too enthusiastically in our efforts to counter the blues.

Unnaturally strong explosions of synthetic experience and sensation and pleasure evoke unnaturally strong degrees of habituation.... Our tragedy is that we just become hungrier." In short, there are advantages to steering for equilibrium initially, rather than always reaching for more stimulation to cope.

Your limbic system is not equipped to understand that there can be too much of a good thing. It just keeps rewarding you to do the same unrewarding things because they register as things that once served your ancestors[19]. A "fix" just positions you for a continuous cycle of highs, more lows, and a search for more highs. Many of us spend much of our sex lives caught in this cycle—with no obvious way out.

The Power of Equilibrium

We have talked about how roller coaster levels of dopamine can break couples apart, but there’s also something holding couples together. The neurochemical that binds couples together is oxytocin, the "cuddle hormone" or "bonding hormone." Without it, we could not stay in love. Falling in love is associated with a soup of neurochemicals—like adrenaline, which makes your heart race, and, as we have mentioned, dopamine, which makes you crave your beloved, and low serotonin, which can make you obsessed with someone. But the heartwarming, loving, "gushy" aspects of love are probably due to oxytocin.

Oxytocin has various functions in the body, such as inducing labor contractions and milk ejection, but from evolutionary biology’s perspective, its main behavioral function is to bond us to our children for life. It also serves to bond us to our mate…at least long enough to fall in love with our child so that it has two caregivers for its long childhood and adolescence. Friendships are also built on oxytocin, and can be quite deep bonds.

Yet, what happens to friendships that turn into sexual relationships? Often things change for the worse. This change is an excellent example of the post-sexual satiation neurochemical shift, or hangover, kicking in. Oxytocin and dopamine are the yin and yang of bonding and love. Dopamine furnishes the kick, oxytocin makes a particular mate appealing, in part by triggering feelings of comfort. You need both acting on the reward circuitry[20] at ideal levels to stay in love. In experiments, if scientists block either oxytocin or dopamine, mothers will ignore their pups.

There's evidence that these two neurochemicals stimulate each other's release[21], so if one is low, it affects levels of the other. As sexual satiation plays havoc with dopamine, lovers can end up with a double-whammy effect on their precious emotional bonds. Low dopamine (or dopamine receptors) alone interferes with feelings of love, and it may reduce oxytocin levels or the brain's sensitivity to oxytocin. As things go sour, something interferes with oxytocin's bonding effects. It's likely that it's (temporary) low dopamine, or reduced sensitivity to it.

The good news is that making love while avoiding sexual satiation is the loophole in biology’s plan for our love lives. This is the secret that the ancient sacred-sexuality sages[22] stumbled upon. Making love with lots of affection, without the dopamine-driven highs and lows of conventional sex, seems to keep neurochemical levels balanced.

There's some evidence that the more oxytocin you produce, the more receptive to it key nerve cells become. This is the opposite of dopamine. In addicts, dopamine receptors start to decrease as the nerve cells protect themselves from overstimulation. Addicts then need more and more of a drug (more and more dopamine). Luckily you don’t need an ever-increasing "fix" of oxytocin to maintain the sparkle in your romance. Daily bonding behaviors can make your partner look better and better[23]—at least to you. This is why daily affection, with less orgasm, can strengthen your bond with your mate.

Oxytocin is associated with significant benefits, both emotionally and physically. In fact, oxytocin may be the answer to the question, "What is the mechanism by which love and affection positively affect our health?" Consider the following research:

Oxytocin reduces cravings. When scientists administered it to rodents who were addicted to cocaine, morphine, or heroin, the rats opted for less drugs, or showed fewer symptoms of withdrawal. (Kovacs, 1998 )

Oxytocin calms. A single rat injected with oxytocin has a calming effect on a cage full of anxious rats. (Agren, 2002)

This quality of oxytocin explains why companionship can increase longevity—even among those who are HIV positive (Young, 2004). Or speed recovery: wounded hamsters heal twice as fast when they are paired with a sibling, rather than left in isolation (DeVries, 2004).

It may also explain why, among various species of primates, care-giving parents (whether male or female) live significantly longer. (Cal Tech, 1998 )

Oxytocin appears be a major reason that SSRI’s [Prozac-type drugs] ease depression, perhaps because high levels of cortisol are the chief culprits in depression and anxiety disorders. (Oxytocin counteracts cortisol's effects.) (Uvnas-Moberg, 1999)

Oxytocin increases sexual receptivity and counteracts impotence, which may be one reason why this other way of making love remains pleasurable. (Pedersen, C.A., 2002), (Arletti, 1997)

However, do not think that spraying oxytocin up your nose, or taking sublingual tabs will in any way reproduce the bonding benefits described here and elsewhere. These effects only occur when precise amounts are released in very specific brain structures. Flooding the blood and brain with oxytocin will cause unwanted side effects [27]and may produce counterproductive mood and perception shifts.

Again, oxytocin reduces cravings and increases sexual receptivity. This allows making love without orgasm[28] to be surprisingly satisfying. The affection is always there, flowing between you and your partner. When we tiptoe around dopamine’s highs and lows, we encourage balance and clear perception of each other. We see each other as sources of safety and pleasure, not as sources of recurring stress with brief moments of sexual pleasure. The real magic of love happens at a neurochemical level—and we can choose balance in order to foil the extremes of our genes' plans for us.

Again, the following two articles update key aspects of this page Your Brain On Sex:

If you would like to learn more about a way to make love that sidesteps humanity's built-in separation mechanism and makes the most of attachment (oxytocin) visit Karezza Korner[30].

For more on the effects of today's hyperstimulating Internet porn on the brain visit Your Brain On Porn[3].

1. Oxytocin rises in rats' brains for hours after mating. It appears to make them engage in riskier-than-normal behavior—perhaps so that they seek new mates. (Unlike humans, they are not pair bonders.)